Grain farming in the United States is where most of the interest is currently for cover cropping. The goal is to have plants growing on the land throughout the frost free period and allowing living roots to feed the soil biology, cycling nutrients without losing them through erosion, volatilization, or leaching. For livestock producers, having perennial forages in rotation create this environment just by nature of the operations. Livestock producers can benefit economically from having plants growing during the full growing season and keeping the soil covered.
For cover cropping to work for grain producers, there are some additional challenges. First is the economics. A cover crop without including livestock may be hard to pencil in the exact revenue it will generate. Fixing nitrogen, breaking up hard pan, helping smother weeds, increasing organic matter, all do not write a cheque to the producer that year. Green manure plough downs work at adding nitrogen, organic matter, and controls weeds, but takes a year of production out of cash cropping.
Another option to get cover crops incorporated into a traditional grain field would be to pick early maturing crops, opening up an option of seeding cover crops after the crop is harvested, using frost tolerant species like turnip, radish, collards, or kale. Or go the other direction, using a spring frost tolerant cover crop, then delay seeding an early maturing crop that is seeded late. This could be a fall seeded cereal that is terminated before spring seeding, using hairy vetch that will normally overwinter, or dormant seeding a species that will tolerate spring frosts, produce early biomass, but is still easy to terminate, like fababean.
A different angle is to intercrop two or more species in the spring. They could mature at similar times, or grow at different heights so they do not interfere with harvest. Producers have played with canola and peas, chickpeas and flax, or oats and flax which would be harvested, then separated. The other intercrop would use flax and winter triticale, wheat and red clover,
or winter wheat and Persian clover.
The twist would be to broadcast the second crop into the cash crop after the cash crop got a head start. This way the cash crop will not have to compete with the companion crop. The companion species will have to tolerate shading and the competition from the cash crop. Crimson clover is know as one of the best clovers to use in this situation. Radish has been used also, broadcasted into a standing crop as the crop is starting to set seed. Radish can start bolting forty days after emergence, so the timing is more critical. Radish seed must be seeded so the cash crop is harvested before the forty days. Normally, for cereals and canola, it is during flowering. The concern is if the harvest is delayed, radish stems may have to be handled by the harvester.
Another way to incorporate cover crops into your management system is to talk to neighbour with livestock to see if there is an opportunity to work with them. They supply the livestock and management, you supply the feed. Water will be one of the limitations, and fencing is the other. Fencing may be the easier of the two to address. Grazing animals is one of the quickest ways to bring soil health to the land. For example, if radish was broadcasted into a wheat crop, the radish plants are high relative feed value and protein, the wheat straw is low feed value and protein. Livestock will graze both the radish tops and straw, making their own rations. The radish tap root will drill down, recycling nutrients that may have leached deeper into the soil profile, break up hard pan, and provide a high feed quality. Radish tops are too rich for cattle, so they will look for roughage, namely wheat straw. The animals will graze the residue, making it “disappear” and reappear as manure. Under years of poor spring moisture or rotations that require summerfallow or chemfallow, cover cropping is an attractive option, from the soil health standpoint. Targeted tillage is not a bad strategy. Targeted tillage is performing a tillage operation with a goal. It should minimize total destruction of the entire rooting system, or occupy the entire A horizon. Residue should remain on the surface. Tillage has been described from a soil microbe viewpoint like a tornado ripping through a trailer park. There are advantages of some tillage such as adding air into the soil, incorporates MOG (matter other than grain) or some of the residue, and stimulates the bacterial population in the soil. Recreational tillage, or tilling the soil black, on the other hand is quite destructive. There will be no cover, microbes are disturbed especially the mycorrhizae fungi, soil is dried out, and nutrients are lost through erosion and volatilization. We have seen a sixty pound difference in land that was worked lightly in the spring, then maintained cover compared to conventional summerfallow. When soil is worked during the heat of the summer, soil microbes are killed and the nitrogen in their cells is lost into the atmosphere. By keeping the microbes alive and active, nutrients are kept in the soil rhizosphere.
Managing residue is one of the advantages that cover crops can offer. In fields with a lot of wide carbon:nitrogen ratio residue, adding a species with a tight carbon:nitrogen ratio will help rot the residue quicker, like adding radish into wheat stubble. On the other hand, crops that provide low residue and may create an erosion issue, like lentils, adding a crop like fall rye, winter triticale, oats, buckwheat or sunflowers could add ground cover. The issue would be herbicide residual may influence what species can be used.
The longer the soil has living roots in it, the better it is for the microbes in the soil. As the plant is growing, it will be leaking sugars into the soil, feeding the soil life. Keeping tillage light and shallow will preserve an environment for fungi. It is amazing how quickly soil life improves when using those two strategies. Earthworm populations recover quickly if allowed to do their thing, and having a healthy fungal population.
Dr. Jill Clapperton said the best way to test the soil health is to monitor earthworm populations. They will move in the soil profile based on temperature and moisture, but to see five earthworms in a 15 centimeter by 15 centimeter by 15 centimeter (six inch by six inch by six inch) cube of soil, is a goal. Anything less means more high quality organic matter needs to be added. Earthworms and other soil organisms love to eat fungi. They are full of micronutrients and complex carbohydrates. Enemies of fungi are high disturbance deep tillage, use of non fungal friendly crops, and over use of systemic fungicides. With dropping numbers of fungi the soil, earthworm numbers are negatively affected.
Dr. Kristine Nichols asks the question, is your soil on a donut diet? The basis of the question is, if a person eats nothing but donuts, the person’s health will be in trouble due to obesity, diabetes, lack of energy, prone to disease, and other health issues. By eating a diet rich in diversity creates the cornerstone of a healthy lifestyle. Same goes for the soil. To feed the
soil microbes two crop types in a rotation, soil life is then selected to only the species that will consume that specific residue. By including a diverse rotation, or adding a cover crop to add to diversity, more diversity in soil organisms will be supported in the soil. The more diversity supported, the less issues of certain species dominating the total population, namely the disease causing organisms.
One of the quick outcomes of cover cropping is increased organic matter. Research is now attributing a larger importance on microbes helping to build organic matter levels in our soils. The increase in organic matter is important because the soil higher in organic matter will hold more water, allow more water to infiltrate, allow good soil aggregation, allow easy rooting, provide shelter and food for soil organisms, and hold nutrients. The higher the organic matter, the more food to support soil microbes, the more activity in the soil, and the more nutrients are able to be cycled. Most blends for grain producers are usually simple blends, maybe one to three species targeted at soil improvement, either chemical or physical. Rotation concerns must be considered, watching for species that may overwinter or volunteer creating issues the next year. Water use and competitive nature of the species to be added is another consideration.